> module VarParen where
> import Result
>
> newtype Tree                  =  Node [Tree]
>                                  deriving (Show)
>
> %{
>
> Terminal                      =  '(' | ')';
>
> Nonterminal                   =  paren {Tree};
>
> paren  {Node []}              :  ;
>        {Node (x : xs)}        |  paren {x}, '(', paren {Node xs}, ')';
>
> }%
>
> frown ts                      =  fail "syntax error"